The present invention relates to high resolution digital imaging and in particular to a digital x-ray imaging system and method utilizing multiple digital cameras.
In conventional x-ray imaging a photographic film is exposed to visible light produced by a fluorescent imaging screen in response to x-ray energy which has passed through an object, in order to capture the image of the object being x-rayed. The x-rays are passed through the object and impinge on the fluorescent imaging screen, such as a phosphor imaging screen. The phosphor imaging screen converts some of the radiation into a selected spectral component (typically visible light). The exposure of the photographic film to the spectral component from the phosphor imaging screen produces the image of the object on the photographic film.
Recent advances in x-ray imaging however have resulted in filmless x-ray methods and apparatus. Such a system is disclosed in U.S. Pat. No. 5,309,496, entitled xe2x80x9cFILMLESS X-RAY APPARATUS AND METHOD OF USING THE SAMExe2x80x9d, issued to Winsor, which is hereby incorporated herein by reference. In the preferred embodiment of Winsor, a video camera and a frame grabber are used to provide still x-ray images.
However, in x-ray imaging it is desirable to get very high resolution images so that a health care provider could accurately diagnose a patient. The use of photographic films as used in conventional x-ray imaging systems does not provide the high degree of resolution desirable in x-rays. Moreover, the video camera and frame grabber of Winsor do not provide the desired high degree of resolution because in the preferred embodiment video camera and frame grabber implementation of Winsor, an image in analog format is filmed by the video camera and a frame grabber used to capture one or more frames. The captured frames may then be digitized. Because of the conversion of the image from analog format to digital format, the desired degree of resolution may not be obtained. Also, as the video tube of the video camera has a fixed life span, it deteriorates over time and accordingly the quality of the image deteriorates over time, which may be evidenced for example by a decrease in the contrast of the image.
Furthermore, in any imaging system, because of the curvature of the lens (or lens assembly), more light passes through the center of the lens than through the edges. Therefore, the intensity of the pixels in the center is greater than the intensity of the pixels at the edges. Because of limitations of the video camera and frame grabber of the preferred embodiment of Winsor, the pixel contrast and/or intensities cannot be modified on an individual basis and therefore, in the final x-ray image the pixels at the center are brighter than those at the edges.
An alternative structure for capturing images is a CCD (charge coupled device) camera. However, high resolution digital CCD cameras are very expensive and still do not provide the high level of resolution necessary for diagnostic x-ray imaging. Because of the difficulty of obtaining large CCD chips of consistent quality and the cost of manufacturing such large CCD chips, multiple digital CCD cameras may be used in place of a single digital camera. The use of multiple digital cameras is known in other fields. In such applications, different cameras are used to capture different portions of the entire image thereby providing multiple images, which are later merged together in order to create a single image. However, in such applications, a known reference point is added to the original image itself. The different images are merged together using the known reference point. By utilizing the known reference point in the merging process, the combining of the images may be accomplished more efficiently. But this procedure adds unwanted artifacts (the reference point itself) to the image. The presence of artifacts in the combined image would be specially undesirable in an x-ray imaging system because of the degree of accuracy preferred in rendering a correct diagnosis of the patient based on the x-rays.
Therefore, there is a need in the art for a system and method for rendering high resolution digital x-ray images of an object.
There is also a need in the art for a system and method for quickly, accurately and seamlessly combining multiple overlapping x-ray images into a single image without adding unwanted artifacts to the final image.
These and other objects, features and technical advantages are achieved by an x-ray imaging system and method which utilizes multiple imaging sensors to acquire an image from an imaging screen.
In a preferred embodiment, the x-ray imaging system comprises at least two imaging sensors, such as digital CCD cameras, with overlapping fields of view. The digital cameras preferably acquire the image from an imaging screen, such as for example, a fluorescent phosphor screen used in x-ray imaging. The digital cameras are positioned so that the field of view of the digital cameras substantially covers the imaging screen. The use of multiple imaging sensors facilitates increasing the resolution of the image as each imaging sensor can capture a smaller portion of the imaging screen.
In the preferred embodiment, the imaging apparatus also includes a host processor based system comprising camera interfaces for receiving and processing the images from the multiple cameras. Such a host processor based system may be for example, a general purpose computer. A preferred method for combining the overlapping images is preferably implemented by software associated with such a general purpose computer. The method comprises calibrating the x-ray imaging system by combining an initial set of two or more overlapping calibration images of different sizes and orientations. During the calibration process, the amount by which an image is to be offset in order to properly align with another image is calculated. The optimal offsets for joining the images in the overlap region are preferably calculated by determining the best correlation of the images in the region common to each of the images. These optimal offsets may be stored in the computer system and used to quickly combine a subsequent series of images of substantially the same size and orientation as the calibration images.
The offsets for a particular camera setting may be calculated periodically, for example once a month, to adjust for any change in the positions of the cameras since the last calibration. Accordingly, in the preferred embodiment, the offsets need not be calculated each time the multiple images of an x-rayed object are to be joined or combined together, i.e., once the offsets for a particular camera setting using the calibration images have been calculated, the offsets may be used to quickly combine or join subsequent individual images into a single image.
Moreover, in a preferred embodiment, in order to provide seamless joining or stitching of the multiple images, the intensities of the pixels of the individual images in the overlapped region may be adjusted. Any noticeable seam between the images may be removed by gradually merging the images in the common overlapping region. This is preferably accomplished by adjusting the intensity values of the individual images in the overlap region so that there is a gradual transition from one individual image to the other.
Accordingly, it is a technical advantage of a preferred embodiment of the present invention to provide a high resolution digital x-ray imaging system.
It is another technical advantage of a preferred embodiment of the present invention to provide a seamless x-ray image.
It is still another technical advantage of a preferred embodiment of the present invention to quickly, accurately and seamlessly combine multiple overlapping images into a single image.
It is yet another technical advantage of a preferred embodiment of the present invention to combine multiple images without the use of known reference points.
It is yet another technical advantage of a preferred embodiment of the present invention to provide high resolution x-ray images without any undesirable image artifacts.
It is yet another technical advantage of a preferred embodiment of the present invention that each pixel in the overlap region can be modified individually.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.